Adjustable porous bed device



United States Patent Inventor Melvin F. Katzer Danville, Calif. Appl.No. 683,753 Filed Oct. 11, 1967 Division of Ser. No. 442,718, Mar. 25,1965, Patent No. 3,371,714. Patented Dec. 22, 1970 Assignee The DowChemical Company Midland, Mich. a corporation of Delaware ADJUSTABLEPOROUS BED DEVICE 2 Claims, 2 Drawing Figs.

11.8. CI 138/43 Int. Fl5d 1/00 Field of Search 1 38/40- References CitedUNITED STATES PATENTS Auberschek Schroder De Lin Deming Kappel PrimaryExaminer-Laveme D. Geiger Assistant Examiner-Edward J. EarlsAttorneys-Griswold and Burdick, William R. Norris and Theodore Post138/41UX 138/40UX 138/40UX 138/41UX ABSTRACT: A device wherein a liquidis constrained to flow through a porous bed of particulate matter andwherein the length of such porous bed traversed by the liquid isadjustable by means of an open-topped, movable sleeve member containingthe particulate matter. The device is particularly useful for decreasingthe pressure in a flowing polymer solution with minimal degradation ofthe polymer.

ADJUSTABLE POROUS BED DEVICE CROSS-REFERENCE TO RELATED APPLICATION Thisapplication is a division of applicants copending application, Ser. No.442,718, filed Mar. 25, 1965, now U.S. Pat. No. 3,371,714.

DESCRIPTION OF THE INVENTION nozzle, or adjustable valve such as a gate,globe, angle, spiral or pinch valve is used in reducing the pressure ona polymer solution, degradation of dissolved polymer results when thepressure of the solution is decreased significantly across the pressurereducing device. This degradation is evidenced by a viscosity loss inthe polymer solution. Degradation of the polymer can adversely affectits usefulness as a mobility control agent in a water flooding mediumfor the secondary recovery of oil. In other applications, the degradedpolymer is less efficient as a thickener or flocculating agent.

In accordance with the invention, it has been discovered that theproblem of molecular degradation, or viscosity loss, as the result ofpressure reduction on a solution of the polymer, can be substantiallyobviated by flowingthe'polymer solution to be depressurized through aliquid permeable, porous-bed of sufficient length to achieve a desiredpressure reduction. While the invention is not predicated upon anexplanation of thiseffect, it is believed the decrease in the pressuregradient in the direction of solution flow through the porous-bed isresponsible for the improved viscosity retention.

The porous-bed may be of consolidated particulate matter such as asandstone or frits or simply loose particulate solids such as sand,glass beads, finely divided minerals and the like held in place withsuitable retaining means. Porous-beds suitable for use herein can alsobe prepared as coarse fiber plugs of materials such as minerals, glass.or metal, natural and synthetic polymers and the like. For, mostapplications the porous-bed will be at least 1 inch, preferably at least3 inches, long.

Although it is not restricted thereto, the present invention finds amost useful application in the reduction of pressure on aqueoussolutions of high molecular weight, water soluble polyelectrolytes. Byhigh molecular weight is meant 1 million or more.

The invention is illustrated in the attached drawings, in which FIG. 1is a sectional elevation of one embodiment of the invention utilizing aporous-bed of consolidated sand, otherwise termed a sand core.

FIG. 2 is a sectional elevation of a second embodiment of the inventionhaving an adjustable porous-bed of unconsolidated sand.

Specifically, the embodiment shown in FIG. 1 consists of a valve housing3 in the form of a cylindrical conduit which has an entering liquid feedline 7 and a discharge liquid line 8. Sealed within the valve housing 3is a porous-bed in the form of a sand core 5 of consolidated sand,viz.,'sandstone. The essential requisites of the porous-bed arei'nsolubility in and permeability to the liquid on which pressurereduction is desired. These conditions are, of course, satisfied formost applications involving aqueous liquids by sandstone. Theconsolidated sandstone core 5 is held in place within the valve housing3 by means of retaining O-rings 13 and 15. These also aid in sealing thecore 5 within the valve housing 3 to prevent liquid bypassing of thecore 5.

When polymer solution under high pressure is flowed through an assemblysuch as that shown in HG. 1, there is a decrease in the pressure on thepolymer solution. At a given liquid flow rate, the pressure decreaseachieved is in proportion to the length of the sandstone core 5. Suchpressure reduction is achieved without significant loss in the viscosityof the polymer solution. The term viscosity" as applied herein tosoluble e.g., water-soluble polymers, is considered to be a measure ofpolymer molecular weight.

The embodiment of the invention shown in FIG. 2 consists of a housingconduit in which a porous-bed of adjustable length composed ofunconsolidated particulate matter occupies a portion of the liquid flowpath through the housing. Thus the pressure drop at a given flow ratecan be increased or decreased within the limits of the extensibility ofthe porousbed.

The illustrated pressure reducing device consists of a housing conduit21 in the form of a cylinder with spaced apart inlet ports 23 and 22.Within the interior of the housing conduit 21 is a porous-bed, baseconduit 25. The inlet end 29 of the base conduit 25 is covered by aporous-bed,' retaining screen cross member 27. This supports aporous-bed 30. The porous-bed base conduit 25 discharges through thewall of the housing conduit 21 at port 26; At the inlet 29'of theporous-bed base conduit 25 is an extensible sleeve 28. This slidablyengages the outer surface of the porous-bed, base conduit 25. To theextent the brim of sleeve 28 extends above the inlet 29 of theporous-bed, base conduit 25, it provides an adjustable mold form for theporous-bed 30.

The sleeve 28 is moved in or out to adjust the depth of the porous-bed30 by means of a screw 32 acting through a threaded packing nut 33. Thescrew 32 is coupled by means of a rotatable coupling 36 to a yoke 35which in turn is fastened to the sleeve 28. The screw 32 is rotated toextend or collapse the porous-bed 30 by means of a wheel 38. Optionally,any means for achieving linear displacement of the sleeve 28 fromwithout the valve housing conduit 21 can be used.

The porous-bed 30 within the sleeve 28 is constituted by anunconsolidated, insoluble particulate matter such as silica sand or anyother finely divided material insoluble in the liquid on which pressureis to be reduced. In the valve housing conduit 21 is enough sand 43 tooccupy the volume of the porousbed 30 as defined by the sleeve 28, whenit is fully extended in relation to the porous-bed, base conduit 25. Thesand 43 is kept within the valve housing 21 by means of a retainingscreen 46.

To operate the described adjustable valve in the preferred manner, it isplaced in an upright position, as shown, and the sleeve 28 is extendedto provide any desired porous-bed 30 depth. A fluid is then passedthrough the valve assembly entering through port 22 and dischargingthrough port 26. The fluid may be a gas, or a liquid, such as that onwhich the pressure is to be reduced. This fluidizes the sand 43 from itsposition of natural repose in the annulus 40 and, to the extentrequired, the sand flows into and fills the porous-bed 30 from theretaining screen 27 to, or slightly above, the brim of the sleeve 23.

Once the porous-bed 30 has been established, fluid on which the pressureis to be reduced is flowed into the valve housing 21 through port 23.Although good depressurization can be achieved by continuing the fluidflow through port 22, fluid entering port 23 enters the valve housing 21above the level of the sand 43 in the annulus 40 thereby avoidingcontinuously fluidizing the same. The liquid then flows through theporous-bed 30 of sand and ultimately discharges from the valve throughport 26 at a pressure lower than inlet pressure.

If it is desired to decrease the pressure drop at a certain flow rate,the sleeve 28 is depressed by turning the screw 32. The flow path of theliquid through the porous-bed 30 is decreased and, thus, the pressuredrop is decreased. An alternate mode of operation achieves a pressuredrop across the annular porous-bed 41. In this method, the liquid to bedepressurized enters port 23 and exits at port 22.

An important advantage of the pressure reducing device described aboveis its adaptability to back flushing to minimize pressure droptransients due to gradual plugging or settling in the porous-bed 30.

For instance, in the pressure reducing device illustrated in FIG. 2, afluid, which may either be a gas or liquid, is flowed into the valvehousing 21 through port 26 and withdrawn through port 22. Whensufficient pressure is applied, complete displacement of the particulatematter from the porous-bed 30 is achieved. The valve is then ready forre-establishment of the porous-bed 30.

Although the invention was first designed as a pressure reducing deviceto carry out the pressure reducing process of the invention, theapparatus shown in FIG. 2 is manifestly useful as a fluid filter orfluid mixer. The latter function is achieved by feeding fluids ofdifferent composition simultaneously through ports 22 and 23. Wheneverthe porous-bed which may be serving as a filter or means of mixingfluids becomes plugged, the filter bed can be reconstituted as describedabove.

Pressure reduction on a polymer solution, such as can be achieved underthe invention, is useful in the secondary recovery of oil by flooding anoil bearing formation with an aqueous polymer solution. For conveniencethe polymer solution is made up and pressurized at a centrally locatedpumping station. From the central source of supply, the polymer solutionis distributed throughout the oil field through main transmission linesand into a number of injection wells through spur feeder lines. Thepressure at a particular injection well head will often desirably besubstantially less than the available pressure in the main line. As aresult, it is necessary to reduce the pressure on the polymer solution.Manifestly, thispressure reduction can be advantageously accomplishedunder the invention with minimum degradation of the polymer in solutionand thus minimum loss of ability to control mobility of the injectionfluid.

Since the molecular degradation problem is most aggravated in instancesof high molecular weight, soluble, linear polymers, e.g., havingmolecular weights of a million and above, it is manifest that theinvention becomes more valuable in its application to such polymers.

Polymers discovered to undergo molecular degradation as a result ofbeing subjected to sharp pressure gradients, i.e., pressure reductionover short flow paths such as occurs in conventional valves andorifices, include the water soluble polyelectrolytes such aspolyacrylamide copolymers of acrylamide and acrylic acid, polystyrenesulfonate, polyvinylalcohol and polyethylene oxide. Similarly allpolymers soluble in organic solvents such as polystyrene, polyvinyltoluene, polymethylmethacrylate and the like can be expected to undergoshear degradation when subjected to sharp pressure gradients. Ingeneral, polymers obtained by the polymerization of monoethylenicallyunsaturated monomers to provide essentially linear, soluble polymers aremost subject to molecular degradation as a result of large pressuregradients.

By way of specifically illustrating the invention, a 1.25 inch, schedule80 steel pipe 12 inches long was packed with silica sand to form aliquid permeable porous-bed. Stainless steel retainer screens wererigidly secured in front and in back of the porous-bed.

A 0.05 percent by weight solution of an acrylamide polymer having amolecular weight of about 2 million was flowed through the bed in aseries of increasing flow rates which resulted in a corresponding seriesof increasing pressure drops. The viscosity of the polymer solution wasdetermined before and after passing the solution through the porous-bed.

It was discovered in this manner that at a pressure gradient of 300lbs/sq. in. per linear foot of sand bed, the viscosity loss of thepolymer solution was only 0.03 centipoise. In this particularporous-bed, a pressure gradient of 1,000 lbs/sq. in. per linear footcaused a viscosity loss of 6.16 centipoise.

In further demonstrations of the invention, conducted in a mannersimilar to that of the foregoing, exce t that porousbeds of 9 inches, 6inches, and 3 inches in leng were used, it

was discovered that molecular degradation, as evidenced by solutionviscosity losses, is controlled by the magnitude of the pressuregradient and is essentially independent of bed length, except in so faras this dimension of the bed affects the pressure gradient.

In comparing conventional pressure reducing valves with the invention,it was found that a pressure drop of 300 lbs. per square inch across a 1inch gate valve induced a viscosity loss in the same polymer solution ofabout 0.25 centipoise and that pressure drop of 1,000 lbs/sq. in. acrossthe same valve caused a viscosity loss of about 0.45 centipoise.

Benefits similar to those achieved above with aqueous polymer solutionscan also be achieved by reducing the pressure on solutions of polymersin organic solvents over an extended pressure gradient in accordancewith the invention.

In addition to adjusting the length of the porous-bed, the pressuregradient, or pressure change per unit of distance in the direction offlow, can also be regulated by adjusting the liquid permeability of theporous-bed. For example, by in-.

gradient is decreased. For a given flow rate, the pressure reductiongradient is also decreased by increasing the crosssectional area oftheporous-bed. It is preferred to keep the pressure reduction gradientbelow about 1,200 lbs. per square inch per linear foot in any particularporous-bed. In any event, the lower the pressure gradient through theporous-bed, the less polymer degradation occurs.

1 claim:

1. An apparatus whichcomprises a porous-bed of particulate matter, ahousing conduit having at least one inlet and an outlet for flowingliquid, within which housing conduit there is positioned a base conduithaving its outer dimensions smaller than the inner dimensions of saidhousing conduit and having a porous-bed retaining screen cross member,said member covering the cross-sectional area within the base conduit,one end of said base conduit discharging through the wall of the housingconduit and the other end slidably engaging an opentopped, adjustablesleeve, said sleeve being adapted to receive particulate matter throughthe open top thereof to form said porous-bed, and means for displacingsaid sleeve in sliding engagement with said base conduit to vary thelength of porousbed presented to the liquid.

2. An apparatus as in claim 1 wherein the housing contains suflicientparticulate matter to occupy the porous-bed defined within the assemblyof the base conduit with retaining screen cross member and porous-bedlength adjusting sleeve when the sleeve is fully extended in relation tothe base conduit, and I having a secondary inlet below the position ofnatural repose 1 for the particulate matter within the housing conduit.

zg gy UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,5 l8,88O Dated 22 December' 1970 Inventor(s) Melvin F. Katzer It iscertified that error appears in the above-ideritifie'd patent and thatsaid Letters Patent are hereby corrected as shown below:

In column 1, line 9, delete "6.16" and insert 0.16

Signed and sealed this 20th day of April 1971.

(SEAL) Attest:

WILLIAM E. SCHUYLEH EDWARD M.FLETCHER,JR.

Commissionerof Pat Attesting Officer-

